The GC/MS is done to confirm results that are questionable on the first urine drug test.  If the person provides a sample that is diluted then depending upon the testing facility’s policies, the sample can be sent to the lab for further analysis.  For example, if the person smokes marijuana and does not want the THC metabolites to show up in the test they may try to drink a lot of water to dilute the sample and fool the testing facility.  This will not work.  A standard drug test for marijuana has an established cutoff tolerance level of 50 nanograms per milliliter of urine.  Anything urine sample testing above this mark will be identified as marijuana and anything below this mark will not.  There are some substances that may resemble THC in the urine but fall below this cutoff level and will register as a false positive for THC.  This is why a confirmatory test may be necessary.

The GC/MS test will confirm whether or not the unidentified is in fact THC and with the confirmatory test the tolerance level may be lowered to 15 nanograms per milliliter.  There are two parts to the GC/MS test, the gas chromatograph and the mass spectrometer.  The gas chromatograph differentiates the chemical properties between various molecules in the sample. While traveling through the gas chromatograph the molecules of the sample are separated and retained in the column of the device and come off of the device at different times. This is known as the retention time.  The device then captures and ionizes the molecules separately and identifies them accordingly.

(To Be Continued)